A head-up display (HUD) makes an image (e.g., one that specifies vehicle speed, etc.) available on a transparent screen so that the image appears to be floating in space beyond the screen. When appropriately configured, the virtual image is combined with a real view of the world outside, as seen through the screen, so that the virtual image and the real world view appear to be at approximately the same distance.
When used in aircraft, for example, a HUD may enable a pilot to see flight information without having to look away from the world outside the aircraft and without having to refocus on flight instruments.